Laser-based killing of a macroparasite inside its live invertebrate host

A bstract Whether host phenotypic alterations induced by parasites are reversible or not is a core issue to understand underlying mechanisms as well as the fitness costs of infection and recovery to the host. Clearing infection is an essential step to address this issue, which turns out to be challenging with endoparasites of large size relative to that of their host. Here, we took advantage of the lethality, contactless and versatility of high-energy laser beam to design such tool, using thorny-headed worms and their amphipod intermediate host as a model system. We show that laser-based de-parasitization can be achieved using blue laser targeting carotenoid pigments in Polymorphus minutus but not in the larger and less pigmented Pomphorhynchus tereticollis . Using DNA degradation to establish parasite death, we found that 80% P. minutus died from within-host exposure to 5 pulses of 50 ms duration, 1.4W power and 450 nm wavelength. Survival rate of infected gammarids to laser treatment was higher than uninfected ones (62% and 33% at 11 days after exposure, respectively). The failure to kill P. tereticollis was also observed with nanosecond-green laser, an alternative laser source targeting lipid. We discuss the possible causes of amphipod death following parasite treatment and highlight the perspectives that this technology offers.